(a) Field of the Invention
The present invention relates to a sulfonated poly(arylene ether) copolymer, a manufacturing method thereof and a polymer electrolyte membrane for fuel cell using the same.
(b) Description of the Related Art
A fuel cell is an energy converting device that can convert chemical energy into electrical energy by an electrochemical reaction between hydrogen or methanol, which is a fuel, and oxygen or air, which is an oxidizing agent. A fuel cell may include a fuel electrode (anode), an oxygen electrode (cathode) and an electrolyte membrane that is disposed between the two electrodes. Such a configuration is called a membrane-electrode assembly. In such an assembly, the electrolyte membrane can facilitate transport of a hydrogen ion that is generated at the fuel electrode to the oxygen electrode (the conductivity of the hydrogen ion is high) and a role as a partition for preventing fuel from being mixed with oxygen (dimensional stability to hydration is high and the methanol transmissivity is low).
Such polymer electrolyte membranes (PEMs) can be classified as fluorinated PEMs and hydrocarbon-based PEMs. Hydrocarbon-based electrolyte membranes can be produced with polymers such as polyimide (PI), polysulfone (PSU), polyetherketone (PEK), polyarylene ethersulfone (PAES) and the like. Hydrocarbon-based electrolyte membranes can provide advantages of low manufacturing costs and good thermal stability relative to fluorinated electrolyte membranes.
However, to provide hydrogen ion conductivity in a hydrocarbon-based electrolyte membrane comparable to that of a fluorinated membrane, a hydrophilic ion group such as a sulfonic acid group and the like can be introduced into a hydrocarbon-based electrolyte membrane. However, introducing such hydrophilic ion groups can deteriorate mechanical properties because of excessive swelling due to moisture and, which can lower the membrane stability and result in the problem of elution of a portion of sulfonated resin.
To address this problem, water solubility of the electrolyte membrane can be lowered by introducing a crosslinking structure to a raw material resin by covalent bonding to suppress elution of the resin, or fluidity of the polymer chain can be increased by introducing the sulfonic acid group into the side chain of the polymer rather than the main chain of the polymer to improve the conductivity of the hydrogen ion. However, these approaches also present drawbacks including that the conductivity of the hydrogen ion can be undesirably low; in the case of the crosslinking approach, the crosslinking of a large polymer can be synthetically difficult, a membrane manufacturing process using the crosslinked polymer also can be difficult, and mechanical properties of the membrane may not be sufficient because the fluidity of the polymer can be lowered due to an increase in the polymer glass transition temperature (Tg).
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.